Predictors of difficult facemask ventilation:

Beard, lack of teeth, history of snoring or obstructive sleep apnea, higher body mass index or weight, limited mandibular protrusion, decreased thyromental distance, modified Mallampati class 3 or 4, history of neck radiation, older age, male sex.

Predictors of difficult direct laryngoscopy―intubation:

Limited mouth opening, modified Mallampati class 3 or 4, decreased thyromental or sternomental distance, limited mandibular protrusion, narrow dental arch, decreased submandibular compliance (e.g. scarring from surgery, burns, or radiation therapy), limited head and upper neck extension, increased neck circumference, history of difficult tracheal intubation.

Impact aggravating clinical factors of difficult airway management:

- Increased risk of bronchoaspiration, increased desaturation rate, airway tendency to collapse.

- Special populations: children, pregnant, morbidly obese, critical or trauma patients.

- Adverse logistic circumstances: lack of equipment, training, support staff or remote locations.

- Predictors of difficult supraglottic device use or difficult emergency invasive airway (see below).

Predictors of difficult supraglottic device use:

Reduced mouth opening, supra- or extraglottic pathology (e.g., neck radiation, lingual tonsillar hypertrophy), glottic and subglottic pathology, fixed cervical spine flexion deformity, increased body mass index, applied cricoid pressure, poor dentition, rotation of surgical table during the procedure, male sex.

Predictors of difficult emergency invasive airway:

Thick or obese neck, overlying pathology (e.g. tumor, inflammation, induration, radiation), displaced airway, fixed cervical spine flexion deformity, age < 8 years, female sex.